Fix a few items broken during review of scanner + parser:
* Make the scanner retain stale newline state on a rewind (as otherwise it must be able to correctly rewind that too, though it doesn't need it). (Probably should revisit).
* Change StashCode in the builder skip to the zero case, as it crashes for some reason (added TODO).

Also fix:
* Drop test based on constant expression evaluation in main parser
* Support constant defined based on existing constant.
* Type constants as signed.
* Added a check that all used functions are defined eventually.
* Zone allocate strings for simplicity (TODOs to refactor better).

BUG=v8:6090
BUG=v8:4203
R=mstarzinger@chromium.org,marja@chromium.org,vogelheim@chromium.org

Review-Url: https://codereview.chromium.org/2771183002
Cr-Commit-Position: refs/heads/master@{#44200}